Manholes are commonly utilized to provide access to underground sewer and utility lines. Over time, the manhole and associated manhole cover are apt to settle below the grade of the roadway or other surface in which the manhole is formed. This can be caused by various factors such as heavy vehicular traffic, precipitation, a high water table and resurfacing of the roadway. Conventionally, various types of manhole riser and cover adjustment rings have been used to bring the manhole up to grade. Typically, one or more of these rings, which are often composed of recycled polyethylene pipe, are mounted above the manhole to bring the cover to grade. If two or more risers are needed, they are bonded together. However, conventional riser rings often feature very narrow contact surfaces, which do not provide for satisfactory bonding. Accordingly, the known risers remain quite susceptible to separation, cracking and deterioration from heavy traffic, precipitation, adverse weather conditions or high water levels. This can again lead to excessive settlement around the manhole cover, which can create potholes and uneven road surfaces that are both unattractive and disruptive to traffic. Moreover, cracked and deteriorating riser rings can cause water to leak into the manhole. Such water intrusion is likely to progressively increase as time passes, which compounds and accelerates deterioration of the riser(s). In severe situations such as heavy rain storms, this can cause flooding of the underground utility station accessed through the manhole.
Rubber gaskets and coatings have been used to limit water infiltration through cracked or aging manholes and manhole risers. However, conventional gaskets usually provide relatively poor adhesion and little if any structural integrity. Such gaskets require solid and continuous riser contact surfaces which, as previously indicated, most conventional risers lack. Coatings tend to crack or peel. Most coatings are relatively brittle and do not adhere well to the standard riser rings that are commonly used.
Alternatively, rubber rings as well as concrete and brick risers have been utilized. All of these materials remain susceptible to cracking and failure particularly under the harsh conditions and environments to which most manholes are subjected.